The present invention relates to coupling assemblies for conduits or tubes used to carry fluid (e.g., liquid, air, gas, etc.), and more particularly, to releasable coupling devices by which a tube or conduit inserted into the coupling device may be disengaged and withdrawn therefrom. Such coupling devices are particularly useful with hydraulic or pneumatic equipment for automatic operation, the coupling devices being used to make either joints between two tubes or conduits, or joints between tubes and the pneumatic or hydraulic component part of such equipment.
Releasable coupling devices are generally known in the art. Such known devices generally comprise a coupling member having a bore into which a conduit or tube to be connected or coupled thereto is introduced and held thereinplace by action of gripping teeth of a retaining element which is inserted in the radial gap between the bore and the tube. An unlocking member is generally provided which is adapted to release the gripping action of the teeth. The known devices also generally include a sealing or packing ring for sealing the bore and the conduit or tube inserted thereinto to prevent leakage of fluid between the coupling member and the conduit or tube coupled thereto.
The manufacturing process for the retaining element and gripping fingers of the prior art devices has generally included first forming a cup shaped member from a metallic plate, such as for example, by drawing or bending the metal, and then, cutting out the bottom of the cup and portions of the sides to provide a plurality of gripping fingers depending from a completely closed ring shaped member. The formed gripping fingers can be biased further inwardly, such as by bending or if the cup-shaped member initially has inclined sides, the formed gripping fingers may be sufficiently inclined without further bending to provide inwardly biased fingers. Such a manufacturing process often leaves burrs or sharp edges on the gripping fingers which causes the exterior surfaces of the tube or conduit to be scratched or marred upon insertion of the tube or conduit.
Consequently, if the sealing or packing ring is disposed below the elevation of the gripping fingers, i.e., between the end of the bore at the interior of the coupling member and the end of the gripping fingers, as shown for example in U.S. Pat. No. 3,909,046 for "Connector for Fluid Conduits, Such as Semi-Rigid Pipes" issued Sept. 30, 1975 to Legris, the sealing or packing O-ring may not serve to adequately seal and prevent leakage of fluid from the interior of the coupling body around the exterior of the tube, i.e., along the serrated portions of the exterior of the tube. In other words, because of the composition and the materials used and the manufacturing process for making such components, an adequate seal may not be provided by the sealing ring since the sealing ring may not deform to a sufficient extent to fill the grooves in the outer surface of the tube caused by the gripping fingers upon insertion of the tube. As can be appreciated, such an arrangement is disadvantageous where it is desired to prevent any leakage. Further, such prior art devices such as shown in the Legris patent have been found to unexpectedly release or unlock the tube from gripping engagement as a result of vibrations when the fluid pressure is lowered.
Another prior art coupling assembly is disclosed in U.S. Pat. No. 4,021,062 for "Coupling Assemblies" issued May 3, 1977 to Mariaulle. The coupling assembly of this prior art device is adapted to be inserted and cemented in place in the bore of a fitting for coupling a tube to the fitting, and comprises a retaining ring having a plurality of gripping fingers inwardly biased and an unlocking ring between the retaining ring and the conduit or tube to be inserted therethrough. Again, the unlocking ring is operable, on being pushed axially, to spread the gripping teeth of the retaining ring to release the tube or conduit. Two generally different sealing arrangements or embodiments are disclosed in this patent. One embodiment, like that of the Legris patent, has the sealing O-ring disposed below the gripping fingers, and accordingly, is subject to the same limitations and disadvantages discussed above with respect to Legris--namely, the possibility of not providing a complete and adequate seal since the hard packing ring may be incapable of filling in grooves or serrations on the outer surface of the conduit caused by the gripping fingers upon insertion of the conduit. The other sealing embodiment of the Mariaulle patent discloses a fluid tight packing O-ring being interposed either between the unlocking ring and the gripping fingers or between adjacent halves of the unlocking ring so that the axial unlocking force is transmitted through the packing ring. Accordingly, the axial unlocking force must be greater than is normally necessary to cause unlocking of the gripping fingers since part of the force is dissipated in or absorbed by the non-rigid, deformable packing O-ring. Thus, this sealing arrangement is also disadvantageous as it is more difficult to cause disengagement of the gripping fingers from the conduit or tube.
Some of these limitations and disadvantages of the prior art are overcome by the device of the aforementioned application Ser. No. 912,003 now U.S. Pat. No. 4,440,424. In that application, there is disclosed an improved releasable coupling device in which the unlocking collar is axially movable relative to the retaining ring for direct engagement with the fingers upon axial movement towards the fingers to force a plurality of fingers radially outward to cause disengagement of the gripping portions from the tube and in which sealing means are positioned axially between the gripping portions of the fingers and the open end of the fitting for sealing the tube in the fitting. The sealing means comprise a fluid tight packing ring fitted in the opening above the retaining ring between the inside wall of the opening and the outside wall of the unlocking collar, and a continuous dimple or bead around the inside circumference of the unlocking collar which is adapted to engage the outside surface of the tube which is inserted into the opening of the fitting. In this way, the problem of providing adequate sealing of serrations or grooves in the outside of the tube caused upon insertion into the fitting is avoided since the sealing means is positioned above the gripping portions of the fingers and thus above the elevation of any possible serrations.